Pixel 2005 – SummaryL. Rossi 18-Sep-2005 Pixel 2005 summary The workshop has tried to cover “all...

Pixel 2005 – Summary L. Rossi 18-Sep-2005

Pixel 2005 summary

• The workshop has tried to cover “all about pixel detectors”, looking at: today (mostly hybrid p.) and tomorrow (mostly integrated p?) in HEP non-HEP applications (biomedical, astronomy,…) “other-then-silicon” sensors

• Some statistics: 50 talks and 19 posters

~half of the talks are on hybrid pixel or related to, this represents the work of ~50 labs and large investments for construction.

• evolution of the field Compare with Pixel2000 workshop (Genoa) % of talks dedicated to hybrid pixels decreases (85%50%). Partly due to a

stop of one project (BTeV), but also indicating that hybrid pixel is a mature technology and the challenges are now in:

Integrated solutions (MAPS, DEPFET, PCCCDS,,…) New material (mostly for non-HEP applications) spin-off activities (pixels start to be competitive in some…)


biases

• Make a conference summary talk is not easy (the last presentation was few minutes ago…), make it of a workshop (more discussions) is even more difficult… I have privileged new results (general bias), even when old results were

more relevant I have privileged what I know better (personal bias) therefore some results (even important) may not have been reported

(especially in the last session), I apologizes for this finally, it would not be surprising if there are mistakes…

• General comments: level of presentations quite good and nobody run overtime significantly,

that’s good. I would nevertheless advice to reduce # of talks next time Even if the summary talk will be done by somebody else...

level of invited talk excellent, I have learnt a lot. Some of those have been very useful to understand fields where pixel may bring (or get) some contributions.

I would have appreciated more problems presented and discussed.


Hybrid pixel

• Mostly reports about status of construction of three detectors (ALICE, ATLAS and CMS) all to be operated at LHC.

• First time in Pixel conf. that we can hear reports about detectors in (more or less) advanced construction status, not just prototypes.

• Use in experiment of hybrid pixel designed for LHC has been already anticipated by NA60. M. Keil reported about the improvement in vertex reconstruction

Beam Trackersensors

windows

• Used ALICE and (for high intensity runs) ATLAS chips and modules


• Also reported improvement (23 instead than 80 MeV) in +- invariant mass reconstruction.

S = 370000 1400(35% of collected statistics)

NA60In-In 158 A GeV~35% of collected

statistics

• all that was expected, but nice to see…


ALICE

• Less rad-hardness problems than ATLAS&CMS, challenge is transparency (<1% X0/layer is the design aim): Thin detector and thinned electronics

yield penalties (also in flip-chip)

Thin services (multilayer Al on kapton) Central part Al/kapton, then Cu/kapton

1st sector out of 10

Riedler


Thin mechanical & cooling support Very sophisticated CFRP shapes to

host modules with minimal mass

• Prototype detectors tested on beam

and simulation tuned to data (cl.size)

but still without B-field (Elia).

• Production of all critical parts started, yield of (large) chip is good (52%) and already 3900 dies have been tested.

• Still to tune on the flip-chip yield (now 64%)

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Pepato


ATLAS

• Most advanced (~50% modules built), start to worry about possible beam accidents.

• Gemme demonstrated that pilot beam accidents (the only acc. LHC experiments should in principle worry about) should not damage ATLAS pixel modules. An experiment was done with PS extracted bunches of 42ns and 1011 p, grazing a pixel module. This corresponds to >30 times the energy released by a beam accident and did not harm the pixel module (so some safety factor…)

• Andreazza presented a detailed analysis of test beam results of irradiated (to 500 kGy)production modules. New results on trapping indicate a carrier lifetime:

e = 4.1±0.3±0.5 ns


• High intensity operation has also been tested and overall losses are proven to be small even at the expected high luminosity in the B-layer.

Drop in efficiency of 1%starts to be seen at occupancy >0.21 hits/cp/bx

B-layerB-layer


• Peric described in detail the ATLAS pixel FE chips now fully fabricated and tested (average yield 82% on 250 wafers).

• Design specs have all been met (also thanks to many global and local tuning bits).

• Some further options have been included and worth noticing. PH information through ToT, self-trigger capability both are important for detector understanding and calibration.

• A trick to recuperate “low (i.e.late) hits” has been implemented on chip and can be activated when needed.

5 0 0 0 1 0 0 0 0 1 5 0 0 0 2 0 0 0 0 2 5 0 0 00

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2 4 6 8 10 12 14 16 18

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80

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120

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160

027,5055,0082,50110,0137,5165,0192,5220,0


CMS

• Is about to begin production

• Kaestli presented the test results on PSI46v2 the “production” version of the front-end chip (including analog data transmission).


• Erdmann showed results of modules built with PSI46v2 in high intensity beam (108/cm2)@PSI

• . not fully satisfactory and there is some need for periodic reset of the chips. Analysis very new, may need some more thinking to sort out the problems (or some re-design?)


Bump-bonding

• Several firms active in the field (reports from AMS (now SELEX), IZM,VTT, “PSI”) Have been possible due to the volume of placements related to the the LHC

projects (~50k), but this still needs close follow-up from experimental groups to optimize process and yield

• Alimonti (for INFN and SELEX) reported a yield of 68% (before rework) and 86% after rework at a production rate of 25 16-chip ATLAS pixel modules/week (now 800 modules done). Reasons for failure are multiple

and often difficult to identify, but

possible only if access to the full

production chain is available Rework is mandatory in these

yield situation. Still valuable even in

the substantially higher yield obtained

at IZM (Fritzsch) where 91%98%.


• Rohe presented the in house bump-flip capability developed at PSI based on In + reflow, bump yield better than 99.9% (flip-chip and rework yield still need more statistics).

• Solder bumping has been discussed by Savoilainen (VTT) who worked for ALICE and LHCb and presented prescriptions on yield optimization throughout the whole process.

• A very interesting overview of the bumping process and problems has been presented by Wolf (IZM) who went through all the possible techniques that are industrially applicable (but In).


• Electroplated bump deposition is the present choice for high density bumping and half of the ATLAS pixle modules have been fabricated with this technique.

• Future trends require abandoning Pb and trials are being done to define the metallurgy of a leadless process.

• HEP is a small special part of a large world bump market (~0.5%) and we have to follow the trends.

• The amount of information provided by Wolf is quite impressive and indicate the complexity of the problem

• Two points are worth mentioning: IZM is building modules for HEP

• w/good yield and in large #

IZM is willing to continue collaborating with HEP.


Radiation hardness of sensors

• At fluences up to 1015cm-2 (Outer layers of a SLHC detector) the change of depletionvoltage and the large area to be covered by detectors is the major problem.

CZ silicon detectors could be a cost-effective radiation hard solution (no type inversion, use p-in-n technology)

p-type silicon microstrip detectors show very encouraging results: CCE 6500 e; eq

= 41015 cm-2, 300m, collection of electrons,

no reverse annealing observed in CCE measurement!

• At the fluence of 1016cm-2 (Innermost layer of a SLHC detector) the active thickness of any silicon material is significantly reduced due to trapping. The promising new options are: Thin/EPI detectors : drawback: radiation hard electronics for low signals needed e.g. 2300e at eq 8x1015cm-2, 50m EPI, …. thicker layers will be tested in 2005/2006 3D detectors : drawback: technology has to be optimized ….. steady progress within RD50

Conclusions from the very complete and detailed review of Moll


Deep(er) submicron electronics

• Yarema presented (for Mekkaoui) the FNAL test chips realized in IMB 0.13m to understand the technology as a first step for a new FE chip design

• Results are encouraging and we may aim at smaller pixels for new LHC b_layers (noise=33-66e thr=718-1160e and (thr)=93-170e) or other use

• Interesting (and worth further investigations) the 90Sr signal got out of a triple N-well diodes implanted in the matrix.

2000 e- signal


CCDs

• Bosiers made an excellent overview of CCD issues, showing (amongst many other interesting things) that CCD can also be pretty fast in image capturing (need local buffer), still not so much in data transfer.

“An image sensor which captures 100 consecutive frames at 1000000 frames/s”, T.G. Etoh et al., IEEE T-ED, vol. 50, January 2003


• Quite some debate about CCD vs CMOS (for image applications). This is a question since long and not solved yet. Pro’s and con’s have been be listed.

• CMOS+ Low readout noise (line

frequency)

+ High-speed (parallel processing)

+ System-on-chip

+ Radiation hardness

More complex design

Expensive mask sets for 0.18m and below

• CCD+ Perfect image quality

+ High fill factor

+ Low dark current

+ Signal processing in charge domain

Radiation hardness

Read-out speed


• Stefanov showed that the read-out speed limitation can be largely improved with P(arallel)C(olumn)CCD

“Classic CCD”Readout time

NM/fout

N

M

N

Column Parallel CCD

Readout time = N/fout

M

• 60 e noise measured with sensor and column-parallel read-out @ 1 MHz

• There are still some gain variation over the matrix (a new version under design) and the rad-hardness to measure…

PPCCD bumped on CMOS ASICS


Medical imaging

• Overdick illustrated the status of the art of industrial production of medical imagers (especially tomography, but also mammography and dental x-rays).

• Even if the field is moving to Direct Conversion (DICO) devices (like pixels) and to higher data throughput, I got the impression that there is not much phase space for pixel detectors there. Competition with flat panel sensors, CCDs and other well established detectors does not leave much room.

• Energy resolved x-ray in pixel counting devices may be a window of opportunity.


• Finger made a detailed and interesting overview of the IR astronomy sensors Quite challenging requirements

Fast, low noise (few e-) @ T~80K with good QE over 0.66-2.5m, minimal interpixel cross-talk and …need fancy sensors.

Astronomy & DEPFETs

ShackHartm ann

Autog uid er

Curva tureSenso rs

• HgCdTe grown by LPE on CdZnTe substrate

• Pixel size 20 m• 16 parallel outputs• Pixel rate 400KHz• Frame rate 1.45 Hz• 3-side buttable• Multilayer ceramic mother board

on metal pedestal• Reference cells included in video data stream• ESO is building 256 channel

data acquisition system (IRACE)

Example of a 2kx2k array for VISTA


• Frame store pnCCDs (Meidiger) for x-ray detection in astronomy (mission ROSITA to detect 50000 new sources of <2 KeV and measure dark energy/matter in universe).

• pnCCD: msec time resolution, 450 m fully depleted, 75 x 75 m pixel 256x256 array.

–

• For future: avalanche pnCCD for single optical photon counting (i.e. an avalanche amplifier added to the on-chip FET). To be backsided illuminated through thin homogeneous window.

–Very good energy resolution: 48eV(@277 eV)133 eV(@ 2 KeV) running cold (-80C), does not degrade much with T up to ~-25C.

20 frames/s, -75C


Pilatus

• Hybrid pixel used for x-ray diffraction studies in PSI on protein cristallography (Henrich )and metallurgy (Tokoyawa).

Thaumatin electron density map

Resolution: 1.4 Å

γ220

α211

γ311

α200

α211 α220

(c) ～ 600℃

α200

γ220

α211 α220

γ311

(d) ～ 500℃

(e) ～ 400℃

600C

400C

500C

Time resolved diffraction pattern, to study crystal

formation in welding


CMOS sensors

• Nicely summarized by Winter.

• CMOS s. provide a good balance between granularity, speed, radiation hardness and material budget and may find their application in future accelerators (e.g. ILC)

• Signal created in the O(15m) thick epi-layer and collected by diffusion in O(100 ns).

• Electronics can be integrated on chip

• Industrial product (potentially cheap and good fab procedure established)

• The first detector was MIMOSA(s), now also CAP (for Belle upgrade) both have been qualified with particle beam and work fine (S/N~20-30) (see Contarato and Varner, respectively).


• Recent significative progress on radiation damage (depends on design and on fabrication process)


• This solution better insulates (through the deep n-well) the sensor cell from digital signal traffic and offers the possibility of implanting complex logic in the pixel cell.

• Preliminary results: 1500 e- collected in 50 ns. S/N~10 due to mismatch between sensor and electronics it is expected to rise to 30 in the next generation of the chip.

• Virtue: can (in principle) implement complex trigger functions on chip.

• First results on a triple-well CMOS MAPS has been presented by Rizzo, it uses 0.13m process from ST.

Landau peak 80 mV

1250

2200

3000 (e-)

saturation due to low energy particle.

Threshold set cuts this region


New sensor material& developments

• Fiederle made an exhaustive overview of CTe and CZT detectors and fabrication (included supplier info). processing of contacts and passivation (difficult)

Note: bulk material sensitive to T In bumping (low T and high density) or Au-stud or z-bond (polymere bump-bonding) both

limited to 200m or other exotic techniques.

• A lot of semiconductor engineering is needed to improve the material quality. Progress, but slow.

• Some material quality problem is still there for diamond (sometimes good, not always) Kagan showed that (for good

samples) the charge collection can be 25ke for 0.8mm tickness and that 300 m diamond still gives ~2500 e- after 500 MRad (silicon?)


• Sherwood P. gave an inspired talk (with a nice historical introduction) on the 3D pixel detectors and outlined the characteristics that make this design apt for B-layer replacement in super-LHC.

Signal after 1 1015

depletion after 2 1015

• Still some more momentum (more people) needed on this activity to get it a realistic option for such an upgrade


Conclusion

• I have found the workshop interesting and useful.

• I have learnt a lot (expecially outside hybrid pixel) This is possibly because I had to follow all talks to prepare the

conference summary…

• and I have discovered that Bonn is a sunny town with mild weather (this is a preliminary result based on low statistics)

• see you (in FNAL?) for Pixel 2007

Pixel 2005 – SummaryL. Rossi 18-Sep-2005 Pixel 2005 summary The workshop has tried to cover “all...

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